Directional radio transmission system



June 9, 1936- A. e. CLAVIER ET AL DIRECTIONAL RADIO TRANSMISSION SYSTEM Filed Jan. 2, 1932 4 Sheets-Sheet l ATTORNEY June 9, 1936. A. e. CLAVIER ET AL DIRECTIONAL RADIO TRANSMISSION SYSTEM 4 Sheets-Sheet 2 Filed Jan. 2, 1932 [DC 8 A INVENTORS: CM WEE R. H. DARBOQD A TTOR/VEV June 9, 136. A. a. CLAVIER ET AL 2,043,347

DIRECTIONAL RADIO TRANSMISSION SYSTEM Filed Jan. 2, 1932 4 Sheets-Sheet 3 11/ F G. [2 j MEMO ,4. a. CLA V/ER 'RH. DARBORD A i'TORNEV June 9, E1936. 5, QLAVIER ET AL 2,43,347

DIRECTIONAL RADIO TRANSMISSION SYSTEM Filed Jan. 2, 1932 4 Sheets-Sheet 4 FIG.

FIG. 10 I W y I w %f c 41 A.G.CLAV/ER INVENTORs- H DARBORD er%77/I4w w A TTORNEV Patented June 9, 1936 DIRECTIONAL RADIO TRANSMISSION SYSTEM Andr Gabriel Clavier and Ren Henri Darbord, Paris, France, assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 2, 1932, Serial No. 584,364 In France January 21, 1931 5 Claims.

This invention relates to high frequency systems such as signaling systems and more particularly to systems utilizing oscillatory energy of very short or ultra-short wave-lengths.

Up to now numerous systems have been tried for utilizing efiiciently the radiation of a high frequency source or for receiving efficiently the radiation of such a source. Among the systems which have been employed are those having refleeting devices associated with the source, the devices being adapted to direct the radiation of the said source in a predetermined direction. Also various types of wire arrangements have been proposed or used as antennas, either for radiating or receiving high frequency oscillatory energy. Such systems, however, utilize only a comparatively small portion of the high frequency energy which could be used and, furthermoreysuch systems have not been proportioned so as to obtain a maximum efficiency. The present invention relates particularly to means for utilizing efificiently from a transmission standpoint, and economically from an energy standpoint, a much greater portion of the high frequency energy radiated by (or received from) one or more sources of electro-magnetlc oscillations of very high frequency than has heretofore been the practice.

An object of the present invention is to increase the efficiency and/or effectiveness of a high frequency signaling system.

Another object of the invention is to reduce the losses ordinarily incurred in radiating and/or receiving high frequency oscillatory energy, and particularly to increase, in high frequency electrical signaling systems of the type mentioned above, the useful portion of the energy radiated by a source.

According to one feature of the present invention, means are provided in a directional high frequency signaling system for greatly concentrating in a predetermined portion of space such as a solid angle a maximum quantity of the energy radiated by the\said source or sources. Thus, in a system utilizing a source located at the focus of a paraboloidal mirror, the energy radiated from the source is made more intense by placing a portion of a spherical mirror on the axis of the paraboloidal mirror, the spherical mirror being adapted to concentrate a portion of the energy radiated by said source upon the source itself. Similar means may be employed in receiving systems for concentrating upon an absorbing member or members a relatively large portion of the energy present n the vicinity of the receiving system.

According to another feature of the invention, a portion of the radiation of such a source is concentrated in a predetermined portion of space, whereas one or several other portions of the said radiation are concentrated in one or several other directions. In the case in which the said radiation is concentrated .in several beams, one or several of the said beams may be subjected to a 10 movement, periodical or not, so as to sweep over a portion of space more or less large, and/or the several said beams may be differently modulated.

According to another feature of the invention the means used for concentrating the high fre- 15 quency oscillatory energy radiated from one or several sources, or received from a remote station, are proportioned, taking into account, and in some cases advantageously utilizing, vthe phenomena of reflection and/or of refraction and/or of interference and/or of diifractions, so that as large an amount as possible of the energy radiated by one or more sources of high frequency' oscillatory energy is a maximum in a predetermined portion of space.

According to another feature of the present invention the means employed may be adapted to produce a polar diagram for a radiating or receiving system having a predetermined shape.

According to more specific features of the invention, the means used for modifying the distribution of the radiation of a high frequency source may comprise difiraction gratings, or electro-optical systems having multiple foci or auxiliary foci. Such means may be used either 35 solely or in combination with other means such as spherical mirrors for modifying the radiation distribution. Several different messages may be simultaneously transmitted upon a single beam by utilizing difierently polarized waves or different wave-lengths, or by utilizing a combination of the above.

The invention will be more fully understood from the following description taken in connection with the drawings in which: 45

Fig. 1 illustrates a source of high frequency oscillations, or a receiver, associated with a paraboloidal mirror for the purpose of increasing the density of the radiated or received beam;

Fig. 2 illustrates an arrangement comprising a paraboloidal mirror and a spherical mirror as: sociated with a source of high frequency oscillatory energy, the said mirrors being arranged and proportioned so as to increase the radiation of the said source in a predetermined portion of space;

Fig. 3 illustrates a two-way transmission system employing features of the invention;

Fig. 4 illustrates a transmission diffraction grating used for modifying the distribution of the radiation from a source;

Fig. 5 illustrates a reflection grating also used for modifying the radiation;

Fig. 6 illustrates a grating combined with a plane mirror or reflector placed at a suitable distance from the grating;

Fig. 7 illustrates a transmission system comprising a grating and a spherical mirror associated with a high frequency radiating and/or receiving apparatus;

Fig. 8 illustrates a paraboloidal mirror at the center of which there is provided an aperture designed to diverge a portion of the radiation and to concentrate it upon an auxiliary apparatus which may be used for measuring or controlling the radiation;

. Fig. 9 illustrates an arrangement comprising features illustrated in Figs. 2 and 8;

Fig. 10 illustrates the combination of a paraboloidal mirror and a plane mirror, the two being associated with a high frequency receiving or transmitting apparatus;

Fig; 11 shows a two-Way transmission system in which a single paraboloidal mirror at each station is employed to modify the radiation emitted and received at the said station;

Fig. 12 shows an electro-optical system having multiple foci adapted to associate cooperatively a plurality of radiating and/or receiving apparatus.

On the drawings similar elements are designated by thesame reference character.

Referring to Fig. 1, reference numeral I designates a high frequency radiating and/or receiv-- ing antenna which may in the case of a transmitter, for example, be an oscillating doublet kept in a state of sustained vibrations by means of any one of the arrangements described in a copending application Serial No. 5198.256, filed on November 26, 1930 by A. G. Clavier, one of the applicants. The element I is associated with a translation device comprising a transmitter or receiver proper. On the drawings element I is connected to the actuating and controlling electrode 3 of a vacuum tube comprising a cathode 4 electrically heated, for example, by means of a battery 5 and an electrode 6 on which a sufficient potential is applied by means of a battery I. It has been shown in the applicationmentioned above that if the actuating and controlling electrode 3 is brought to a potential sufficient by means, for instance, of a battery 8, cscillatory movements of electrons take place within the tube and these movements give rise to high frequency currents in the radiating element I which acts substantially as adoublet.

When it is desired to use the above arrangement in a transmitter of a telecommunication system the doublet I is energized with high frequency sustained oscillations which are modulated by means of a modulator 9 coupled to the oscillating tube by means of a transformer I 0 placed in the grid or in the plate circuit. When the doublet is used in the receiving system the high frequency field sets up in the doublet currents of the-transmitted frequencies and these currents are usually demodulated or detected by means of a demodulator corresponding to the apparatus 9, the demodulator being coupled to the element I by means of a transformer similar to that designated by numeral I0.

It should be understood that other types of re.- diating elements than those described in the application above mentioned could be used in the place of element I.

ple, the paraboloidal mirror 2, the radiation is increased in front of the mirror, whereas towards the back of the mirror the radiation of the source is practically n11.

In a high frequency transmission system such as a telecommunication system, it is generally desirable to obtain a field of maximum intensity in the predetermined portion of space in which the receiving apparatus is located while utilizing the minimum of energy at the transmitting station. In order to utilize efliciently the energy available it is necessary to increase .so. far as is possible the useful radiation of the source and also to employ the useful radiation as efficiently as practicable.

In order to increase the useful radiation of a source it is practically necessary to act upon the source itself or to so proportion the radiation resistance offered to said source as to obtain the maximum usefulpower from the said source. Moreover, in order to employv efficiently the useful radiation it is important that this useful radiation be concentrated in a relatively small portion of space so that the field created by the transmitter at the receiving station is a maximum. For the purpose of attaining these results there is provided in accordance with this invention in the vicinity of one or several radiating and/0r receiving elements, apparatus which permits the phenomena of reflection and/or of refraction and/or of interference and/or of diffraction to be utilized.

Theapparatus adapted to modify the distribution in space of the radiation of the said sources may conveniently comprise electrically conducting or non-conducting bodies or surfaces whose dimensions and contour are chosen, the diffraction phenomena presented by the system being considered especially, so that the radiation diagram of the system has a predetermined shape, and particularly so that the field set up by the arrangement comprising the source and associated apparatus is a maximum in the predetermined portion of space in which the receiving apparatus is located. In order to obtain the best possible result with a radiation concentrating system such as the paraboloidal mirror shown in Fig. 1, it is necessary to take into account the distribution of the radiation around the source, as well as the diffraction phenomena presented by such a system, for computing the field created where the receiver is located and for finding out the conditions which must be fulfilled to give to the said field a maximum value.

It is known that diffraction phenomena takes place in all the phenomena of optics and prevents the attainment of rigorously punctual images. Even with a perfect optical system the image of v a geometrical point is necessarily a small surface or a small volume according to the manner in which the matter is considered, the dimensions of the small surface or of the small volume being necessarily of the order of the wave-length. In the case of ultra-short waves, for instance of wave-lengths equal to 20 cms. the dimensions of the images obtained are necessarily of the order of 20 cms. Now when it is desired to produce a When the radiating element I is associated with a mirror, for exambeam as parallel as possible the diffraction phe- 76 nomena limits the possibilities in the same way and even if the electro-optical system intended to modify the radiation distribution is I perfectly computed the beam obtained is a diverging beam, The angle of this beam is smaller as the diameter of the electro-optical apparatus (paraboloidal mirror lenses, etc.) is greater. It should be noted that in an electro-optical system comprising a paraboloidal mirror and a very high frequency source of oscillations positioned at the focus of the mirror, it has been determined, after theoretical and experimental studies, that one may consider that the diifraction phenomena does not intervene between the focus of the paraboloidal mirror and the paraboloidal mirror itself. The electric field impinging on the mirror is determined by the nature of the source, doublet or antenna.

The reflection field, at least at the surface of m the mirror, is parallel to the axis of the paraboioidal mirror in view of the geometry of the paraboloidal mirror and of the fact that the resultant of the impinging and reflecting fields must be perpendicular to the surface of the metal. The reflected field mentioned above may be divided into two components, one parallel to the doublet, the other perpendicular thereto for the purpose of determining the field at a great distance in the direction of the axis of the mirror. .This is true since the beam is not exactly a parallel beam, that is, it does converge to some degree. The components of the field perpendicular to the doublet emitted by the different points of the mirror mutually cancel one another at the distant point because of the symmetry of the system. Consequently, the resultant of the fields at the distant point is still parallel to the doublet. It is therefore necessary to determine this resultant taking into account the phenomena of diffraction.

Let h represent the component parallel to the doublet of the field reflected by an element of the mirror, the projection of which element on a plane perpendicular to the axis being ds. After theoretical and experimental studies it has been found that the field which it is desired to determine may be represented by the formula:

in which D is the distance-from the mirror to the receiving station and A is the wave length.

It should be noted that this formula represents some sort of generalization in theapplication of the principle of Huygens according to which every point of a wave surface may be considered as a source from which waves are emitted. The classical case which is the nearest to the one considered here is that of a luminous point placed in front and on the axis of a circular screen, the problem being to compute the luminous vector reflected by the screen at a distant point positioned on the axis of the system. The formula given above applies to this classical case. The

case is not strictly applicable but it does show.

that this formula is in accordance with the usual manner of treating diffraction problems in optics. In optics also the formula given above may be obtained in an equivalent form with the assistance of hypothesis more or less arbitrary. Moreover, it is possible to demonstrate this formula by applying the principle of conservation of energy, but this demonstration supposes, and this is the case in optics, that the incidence and diffraction angles are small. In the optic case the elements ds are substantially perpendicular to the incident and diflracted ray. The case of the paraboloidal mirror is more general in'that in the application of thepreceding formula, the elements ds have been chosen substantially perpendicular to the reflected ray in the direction of the axis.

In the case of a paraboloidal mirror let d represent the diameter of the mirror. Then aperture e of the beam outgoing from the paraboloidal mirror in degrees is given approximately by the formula:

in which A and d are measured with the same unit.

Both of the above equations take into account the diffraction phenomena presented by such a system. By taking into account the distribution of the radiation of a doublet or radiator in various directions and the phenomena of diffraction, it has been found advantageous to select the paraboloidal mirror in such a way that the focal region is in the plane of the opening of the mirror. Letting H represent the field created at a distant point by a system using such a mirror and H the field produced at the same point by a doublet alone the gain g will be:

H 1rd E E The maximum intensity of the field h at a distance D in kilometres is then determined approximately by the following equation:

in which P is the total power in watts radiated by a doublet, d and A having the same signification as that given above and being measured with the same unit of length. It will be seen therefore that, in order to render as large as possible the field at a distance it is necessary that the total aperture of the beam is small and consequently from the equation immediately above the diameter d of the mirror must be as large as possible.

It is obvious that, in accordance with the present invention, the most favorable dimensions can be determined for reflectors of types other than the paraboloidal mirror, the reflectors being provided with the radiating or receiving doublet. For instance a spherical mirror having suitable dimensions with regard to the wave length employed and being centered, for example, on a doublet gives an imperfect image of this doublet due to the phenomena of diffraction by which the image is formed upon the doublet itself. This system functions to concentrate the radiation of a doublet into a solid angle substantially equal to 211' (if the spherical mirror is approximately half a sphere) and consequently approximately all the high frequency oscillatory energy sent in the solid symmetrical angle is employed and the field in a predetermined direction is doubled substantially.

The spherical mirror is preferably chosen so that the reflected beam is in phase with the direct beam. The phenomena of reflection introduces a phase change equal to w; and experiments have shown that there exists another phase change of 1r when the reflected beam passes through the focus or focal region of the spherical mirror, that is, through the doublet or radiator provided at this focus. It results from this therefore, that, in

' the radius of the spherical mirror should be equal at least approximately to a multiple of a halfv wave-length of the wave employed.

It has been indicated above how reflecting devices should be proportioned in order to obtain a maximum efllciency from these apparatus. In this connection it should be noted here that the principles indicated may also be used for suitably proportioning apparatus such as mirrors or gratings which bring mainly into play the phenomena of reflection or diffraction, respectively. This will be explained later in more detail.

The systems above mentioned utilize, for creating a predetermined fleld at one or several receiving stations only a part of the useful radiation of the available sources of high frequency oscillatory energy, In order to utilize a larger portion of the useful radiation of the high frequency sources utilized, one may, in accordance with features of the present invention, associate several reflecting apparatus with one or more sources of high frequency oscillatory energy, the arrangement being such that the field set up in a determined portion of space where is located, for instance, a-recelving station, is a maximum. For example, when a paraboloidal mirror whose aperture corresponds to a solid angle e is associated with a source of very high frequency oscillatory energy approximately only the radiation of the said source comprised in the solid angle a is utilized for transmission purposes, whereas the radiation of the said source comprised in the complementary solid angle 41r-e is not utilized. In order to overcome this drawback one may, for instance, utilize the arrangement shown in Fig. 2 which comprises a paraboloidal mirror 2 and a spherical mirror 2' associated with a radiating and/or receiving element I.

The element l is located at the focus of a paraboloidal mirror 2 and at the center of the spherical mirror 2' which is preferably proportioned as indicated above. It will be seen that with the arrangement shown in Fig. 2 the spherical mirror brings back upon the element I, that is, towards the paraboloidal mirror, the diverging beam which would be radiated by the element I if this element is a source. The spherical mirror cancels approximately the radiation of the element l in the cylinder having for base the aperture of the spherical mirror 2' and for axis the axis of the paraboloidal mirror 2. suppression of this portion of the radiation it may be seen from computation and by experiments that the field at a distance created by the system I, 2, 2' is substantially twice greater than the field created by the system when the spherical mirror is not provided. The diameter of the spherical mirror must not be too large with-regard to the aperture diameter of the paraboloidal mirror since the spherical mirror acts as a screen for the central portion of the parallel beam emitted.

It should be noted that in the system shown in Fig. 2 that portion of the radiation emitted by the source and comprised in the solid angle as determined by the paraboloidal mirror and the spherical mirror is utilized. As a matter'of fact the portion of the radiation emitted by the element l and utilized for transmission purposes is greatly increased with regard to what it would be if the spherical mirror 2' were not provided.

In order to utilize to a maximum the radiation emitted by a source, other arrangements may be In spite of the provided according to the features of the present invention. For example, one may utilize a spherical mirror centered upon a source and a lens dis- P sed at a suitable distance on the axis or the spherical mirror, the lens being adapted to trans- 5 form the diverging beam produced by the spherical mirror into a parallel beam. The lens employed should have a refraction indice as large as possible for the wave-length utilized and in the case of waves of the order of meters or of some decimeters or portions of decimeters lenses of ebonite or wood may be employed. In the case of the combination of a spherical mirror with a lens a portion of the radiation emitted by the source is ordinarily lost but this portion may be utilized according to this invention. For example, a portion of a paraboloidal mirror may be employed which is adapted to direct the radiation which otherwise would be lost in the direction of the receiving station. Moreover, this portion of the radiation may be directed in a different direction from that in which the principal portion of the radiation of the source is transmitted. Also, the portion of the radiation which otherwise would be lost may be directed periodically in acertain number of directions, whereas for example, the main portion of the radiation is constantly directed in the same direction. This last arrangement-is particularly useful in the case of telecommunication systems with ultra short waves whose radiation is periodically directed in a certain number of directions.

Fig. 3 illustrates an embodiment of the invention in a two-way telecommunication system employing reflecting systems of the type shown in Fig. 2. An antenna system with associated mirrors such as the one shown in Fig. 2 may be used either for transmission or for reception; and the transmitters and the receivers in Fig. 3 have been schematically illustrated by means of a portion of a parabola and of an arc of a circle centered on a radiating and/or receiving element.

In the system of this figure the equipment at the station ll comprises a transmitter l2 and a receiver I3 and the installation at the other terminal station l4 comprises a receiver l2". and a transmitter 13'. The three lines parallel to axes of each set of mirrors illustrate the preferred method of relatively positioning the wires connected to the tube associated with the doublet. It will be observed that the wires, in the case of the receiver, pass through the paraboloidal mirror; and, in the case of the transmitter, they pass through the spherical mirror. At each station the arrangement is such that the receiver is 65 located in the shadow of the transmitter of the same station in order to prevent the receiver from being influenced by the transmitter of the corresponding station. The shadow of the mirror is here defined as the region at the rear of the mirror which is unenergized by waves emanating from an antenna cooperating with the mirror. In other words, the rays directly emitted by the transmitter do not influence the receiver at the same station. In practice, in order to obtain such a result, the angle between the transmitting and receiving stations is made equal to 45 and the distance 3 between the said stations equal to about 200 m. Obviously, different angles and distances could be chosen, but the receiving station is preferably positioned in the shadow of the transmitter at each terminal station of the two-way system.

In the systems described above a maximum utilization of the radiated energy (whether it be 75 small or large in amount) is realized. In order to obtain for radiation purposes a maximum amount of high frequency oscillatory power from a source excited under given conditions it is possible, according to another of the features of the present invention, to change the radiation resistance so that the power obtained from such a high frequency source of oscillations, which power depends upon the radiation resistance, may be a maximum. In other words, there is produced a reaction between the source and the apparatus comprising mirrors, lenses, etc. adapted to modify the radiation of the said source and this reaction is such that the power radiated by said source is increased. This may be seen from the following explanation:

Let us consider, for example, a system constituted by a doublet located at the center of a mirror having the shape of a half sphere. Let us term 3, for example the solid angle of emission directed towards the mirror and 61 the angle of emission which is not directed towards the spherical mirror. In the absence of the spherical mirror, the field set up in the angle 3, at a certain distance, is h, and the field set up in the angle 51, at the same distance, is h. If the total power radiated by the doublet is P,

is the power in the angle 5 and is the power in the angle 61. The spherical mirror being associated with the doublet, the field becomes zero in the angle p beyond the spherical mirror and, ifthe radius of the spherical mirror is suitably chosen, the field becomes h+h=2h in the angle 51. The power radiated in the angle 51 becomes four times greater, that is to say 2P, since the field becomes twice as great. The total power radiated is therefore doubled due to the introduction of the spherical mirror. Thus, either the R. M. S. intensity in the doublet remains the same when the spherical mirror is introduced and the total power radiated by the doublet is increased which corresponds, in other terms, to an increase of the radiation resistance; or the R. M. S. intensity in the doublet is modified. At any rate the presence of the spherical mirror modifies the emitting of a tube and this modification may be used advantageously. It has been experimentally determined in this connection that the presence of a spherical mirror does not modify the intensity of the current circulating in a radiator associated with tubes of the type described in the copending application No. 498,256 mentioned above.

The above mentioned consideration supposes the absence of diffraction phenomena but it will be seen that the result remains the same even if the diffraction phenomena becomes important.

Instead of utilizing reflector systems, such as those illustrated in Figs. 1, 2 and 3, one may utilize conducting bodies for modifying the radiation distribution of a given source in order that the said conducting bodies operate substantially as electro-optical gratings. Such a system is shown in Fig. 4.

Referring to Fig. 4, the grating 20 illustrated is a transmission type, that is, the grating transforms a diverging beam into a parallel beam. Inversely it transforms a parallel beam into a converging beam. The grating 20 comprises a plurality of concentrical rings designated by the numerals I5, I6, I I and I8, the rings being supported by a suitable structure I9. The dimensions of the rings or zones I5, I6, I1 and [8 may Geometrically, the dimensions of a zone plate such as the one shown in Fi 4 may be ,determined by means of a plurality of concentrical circles, Ia, I b, Ic, etc. Ii, having their centers at the focus or focal region I. The circles are then cut by means of a straight line XY perpendicular to the axis. The radius or radii of the circles Ia, Ib, lc, Id are such that the following relations are fulfilled:

Such a zone plate is obviously easy to manufacture and is suitable for modifying the radiation of a source or the radiation received from a remote station. Incidentally, such apparatus is evidently capable of very numerous applications in high frequency systems in which wave-lengths are sufficiently small.

Other types of grating may be utilized and Fig. 5 shows, for example, a reflection grating. This grating is similar to the one shown in Fig. 4 but it is proportioned so as to reflect the radiation impinging upon the grating. The grating shown in Fig. 5 may be calculated in the same manner as the grating shown in Fig. 4. That is, to obtain a reflection grating or lens it is necessary to determine the diameter of the metallic zones in such a Way that the following relations may be approximately fulfilled:

The system illustrated in Fig. 5 acts substantially as a paraboloidal mirror, that is, it transforms a diverging beam into a parallel beam. The dimensions of the grating shown in Fig. 5 may obviously be determined by means of a geometrical construction analogous to the one illustrated in Fig. 4; in the present case the relation to be fulfilled is as follows:

It is useful to know that the grating of Fig. 5 is the complementary grating to the one shown in Fig.- 4.

Fig. 6 shows a grating 20 and a plane mirror 2| associated with a source I of very high frequency oscillatory energy. The central zone and the metallic rings of the grating 20 deflect the energy emitted by the doublet I towards the desired direction. According to the construction of the grating itself, none of the deflected rays so that the waves which pass through the hollow rings and are returned by mirror 2| travel a supplementary path equal to which represents the distance to and from the grating and the plane reflector 2|. Conse- 'quently, the directly propagated rays and those returning through the hollow rings are in phase, and the field at a distance in the direction of the axis is increased.

. Systems utilizing zone plates such as those described above may be utilized in high frequency transmission systems such-as signaling systems. Fig. 7 shows an example of such a system. On the left of this figure a transmitting element I is associated with a spherical mirror 2' for tlie purpose of transforming the radiation from the element l into a diverging radiation comprising the solid angle (0. The portion of this radiation located in the angle to is transformed into a parallel radiation beam by means of the transmission zone plate 20. This parallel radiation beam is received by the receiving station on a transmission zone plate 2|! which transforms it into a converging radiation beam focused upon the receiving element i' which is located at the focus of the spherical mirror 2". A system of this nature is more easy and economical to make than a system comprising lenses in place of the zone plates 20 and 20'. It should be noted that in the system of this Fig. 7 the radiation of the doublet comprised in the solid angles an and w: is not utilized. These angles are relatively small in view of the fact that the zone plate 20 has a. relatively large diameter; and the loss of high frequency oscillatory energy in the portions of space corresponding to these solid angles is negligible.

The diffraction gratings described up to the present are plane or flat diffraction gratings but, obviously, zone plates having surfaces other than plane surfaces may be employed to modify the radiation emitted or received by the element I.

Fig. 8, for instance, shows a parabololdal refiector 2 having in its center an aperture 0: whose dimensions are such that the said aperture operates as a central zone of a transmission diffraction grating, the two fool of which are at finite distances. Such a system possesses great advantages when a parabololdal mirror having a radiating element I located at its focus is employed. For example, it' is often desirable to know the intensity of the radiation emitted and for this purpose a thermocouple 26 is located at the focus i' in order to obtain an indication proportional to the radiation emitted.

To determine the dimensions of the central zone MN the following relation may be used:-

The distance I? is chosen when determining the optical emitting system and the distance I'P is chosen, generally, according to practical considerations. Knowing the distance iPl' and using the equation given above, the most favorable diameter for the aperture 0: may be determined.

At the receiving station generally it is not necessary to provide a controlling wave-meter or a thermocouple and it is best to have the connec tions for the tube pass through, and along the axis of, the parabololdal mirror which is ordinarily fixed in front of the construction housing the controlling and actuating apparatus used for transmission and reception. This is especially true if it is necessary to amplify the received signals by utilizing an intermediate frequency. That is, under these circumstances, it is better to have the signals collected by the doublet and by the receiving tubes pass as directly as possible to the amplifying apparatus. On the other hand, at the transmitting station, a central portion of the parabololdal mirror is used for the measurement of the radiation emitted and in this case the connections for the tube will preferably 5 pass through the spherical mirror.

Fig. 9 shows a transmitting arrangement in which certain features illustrated in Figs. 2 and 8 are utilized. In this figure the paraboloidal mirror 2 is carried by means of member 22 which may be placed underneath the penthouse like structure 23. The parabololdal mirror 2 comprises metallic sheets which have been given a suitable form by a hammering operation at room temperature upon a concrete form or matrix having suitable dimensions. .The sheets thus prepared are placed upon the surface 22 so as to form the parabololdal mirror 2. This mirror has I an aperture a which forms the central zone on a transmission zone plate, the focal regions of which are at finite distances. At the focus of the parabololdal mirror there is placed a radiating element l which is kept in a state of sustained oscillations by means of an apparatus 24 of the type described in copending application No. 498,256 mentioned above. The radiating element l is also placed at the center of the spherical mirror 2' which may be formed by shaping a sheet of copper by a suitable process.

The spherical mirror 2' is fixed upon the support 25 which is itself carried by a pole 26. The electrical connections between the apparatus 24 and the sources of energy, or with the modulator, or receiving apparatus, must be arranged as symmetrically as possible and preferably in the case of the transmitter in the manner shown in Fig. 9, that is, the connections for the tube 24 should be directed towards the apex of the spherical mirror 2', the said connections being arranged so as to be substantially parallel.

In order to'be able to measure the intensity of the radiation emitted by the arrangement comprising radiator 2, parabololdal mirror 2 and spherical mirror 2', a wave-meter or a thermocouple 26 associated with a current indicating device such as a galvanometer is placed at the conjugate focus I of the central zone 0:. Such a thermocouple fulfills, in the case of a transmitting system of the type shown in this figure, a role analogous to that of the antenna ammeter utilized in known types of radio electric transmitters. ceiver an arrangement such as shown figure or in Fig. 5 may be employed.

It should be noted that in the system of Fig. 9 it is 'not necessary that the mirrors 2 and 2' be At the distant cooperating rein this exposed to the open air, and the penthouse struc ture 23 may therefore be closed by means of walls of wood or of glass, or by any other suitable means. Of course, the material used in the walls should be such as tominimize the energy losses which are mainly due to partial reflection when the beam traverses a wall of the penthouse 23. It should also be noted that the radiator in the system of Fig. 9 may be advantageously lo- I cated in a position as high as practicable for the purpose of increasing the optical visibility. This may be necessary in transmission systems utilizing oscillations of very high frequency.

Referring to Fig. an arrangement is illustrated which is particularly suitable for obtaining a beam parallel with, and at a relatively great height above, the surface of the ground. The arrangement comprises a paraboloidal mirror 2 associated with the plane mirror 2'! which may be placed on the top of a tower. It will be seen from this figure that the method of representation employed in geometrical optics has been used. The parallel beam obtained by means of the paraboloidal mirror 2 is transformed into a parallel beam at approximately right angles to the first beam by means of the plane mirror Ell. This plane mirror may be adapted to rotate around the axis of the paraboloidal mirror 2 so that the radiated beam sweeps over a more or less great arc of the circle of the horizon. The mirror 2'! may also be adapted to rotate around an axis perpendicular to the axis of the paraboloidal mirror 2. Also, there may be provided a spherical mirror 2' associated with the element l and an aperture 0 may be provided in the plane mirror 2?. The aperture may be such that it functions as the central zone of a zone plate, or

its diameter. may correspond to the aperture diameter of the spherical mirror 2. To control the radiation emitted by the element i, there may be placed at a suitable point in the beam obtained, a small mirror (not shown on the drawings) adapted to direct a portion of the radiation towards a controlling apparatus such as a suitable wave-meter.

Fig. 11 illustrates a practical and economical system for utilizing a paraboloidal mirror as a means for causing the convergence of a received parallel beam upon one doublet, and for converting into a parallel beam a portion of the diverging rays transmitted from a nearby doublet. Thus the parallel beam received at the station at the left from the doublet i1 is concentrated by means of mirror 2 on the doublet l'1. The energy radiated by doublet l is changed into a parallel beam partly by means of thesame mirror 2. The lens 28 which is similar to the reflection grating 26 illustrated in Fig. 5 cooperating with the spherical mirror 2' converts most of the en-. ergy radiated from doublet I into a parallel beam and the paraboloidal mirror 2 functions to convert the portion of the energy which would otherwise be lost into the same type of beam. Similarly, the paraboloidal mirror 21 at the right-hand station concentrates the energy (received from doublet l) on the doublet l, and at the same time assists in changing the diverging rays radiated by doublet 61 into a parallel beam, lens or reflection grating 281 being most instrumental in producing the parallel beam. Independence between the two ways of transmission may be accomplished by choosing the planes of polarization of the radiationtransmitted in two opposite directions or by establishing the two ways of,

E5 transmission upon different wave-lengths, or by any other suitable process, or even by a combinationof the means which have iust'been described. v

Fig. 12 shows an electro-optical systemhaving multiple focus regions which are associated with a plurality of radiating elements. In this figure a plurality of radiating elements I, I1, lnfand I111 are provided and associated, respectively,

' with oscillation'sources S, $1, $11; and S111 which -may beindependent or not. These radiating elements are preferably disposed upon the same axis assuming, of course, that the foci of the system are located upon a common axis as shown in this figure. In the system shown on Fig 12 efforts have been made to utilize the greatest portion of the radiation from the various elements, and for this purpose there is associated with the element l aspherical mirror 2' and a transmission zone--plate 20 designed to have tool or focal regions I and I1 at finite distances. A second zone plate-201 and a third zone plate 2011 are provided which have their foci at finite distances corresponding to the positions occupied by the radiators I1, I11 and I11 and i111, respectively. The system is completed by means of a relatively large end transmission zone plate such as plate 20111 adapted to transform into a parallel beam theradiation emitted by the radiating elements I, I1, I11 and I111. Additional radiators and intermediate zone plates may, of course, be used.

Obviously, the system of Fig. 12 may be used for reception. Furthermore when used for transmitting it may be used for combining in the same beam radiations emitted by a plurality of radiating elements, the radiations having different characteristics whereby the same beam serves to transmit a plurality of signals or messages. Thus, the 'various radiating elements may have different polarizations or they may be arranged to radiate alternately, or they may be differently modulated.

Although in the foregoing there has been considered the simple case wherein the sources of high frequency oscillatory energy is constituted by a radiating doublet, it is clear that other types of high frequency oscillatory energy sources could be used and particularly the various sources of oscillatory energy described in the application No. 498,256 mentioned above could be used. In particular, sources of polyphase oscillatory energy may be used which would allow in some cases several messages to be transmitted upon the same wave-length. It is clear that the various systerns described are illustrative only and that embodiments different from those herein shown and described could be made without exceeding the device connected thereto, a paraboloidal mirror having an aperture extending therethrough, a wave measuring device, said antenna being located in the focal region of said mirror and said measuring device being located in the focal region of said aperture.

3. In an ultra-short wave system, an antenna, a spherical-shaped mirror having a radius equal to a multiple of one half the operating wavelength substantially, the antenna being positioned at the geometrical center of said mirror approximately.

4. In combination, an antenna, a translation device connected thereto, a paraboloidal mirror having a focus in the plane of the mirror opening and a grating at its center, a hemispherical mirror positioned on the axis of the paraboloidal mirror so that its focus coincides with the focus of the paraboloidal mirror, and a wave measuring device located at the focus of the grating.

5. In combination, a transmitting station and a receiving station arranged for duplex operation, said transmitting station and said receivfocus, said couplet being located at said focus.

said receiving station being positioned in the shadow of the transmitting paraboloidal mirror whereby radiation from the transmitting station does not affect the operation of the receiving station.

ANDRE GABRIEL CLAVIER.

RENE HENRI DARBORD. 

